drupal path fix

1. /collections has been URL-aliased to node/2779. Therefore, we won't need
"collections " in menu system(remove $items['collections'])
1.1 remove "$items['collections']" out of menu system will lost 'collections' in navigation bar, don't know why

2. we don't need function collections_nodeapi since now /collections has been mapped to node/2779. We don't need it to render '/collections' page

3. remove all loader since now we use page callbacks to connect collections and drupal

4. the function of collection_preprocess_page. It will append $collections['template_files'] to $variables['template_files'] which will be used to generate collections pages in theme().

4.1. We need the condition if ( ! isset($collections) ) since collection_preprocess_page could be called without being followed _collections_load which we define collections.